There is a fundamental gap in understanding the physiological mechanisms of age differences in manual motor control. This is an important problem given the rapidly increasing older adult segment of our society. The long-term goal of my research program is to identify the neural mechanisms for age-related declines in sensorimotor function, allowing me to develop and evaluate targeted interventions to prolong functional independence for older adults. Our recent work leads to the intriguing and novel hypothesis that age declines in manual motor function are due at least in part to reduced distinctiveness of cortical sensorimotor representations. We have shown that motor cortical representations devoted to a single finger muscle are larger in older than young adults, suggestive of reduced intrahemispheric distinctiveness. We have also shown that motor representations for a single hand extend across both hemispheres for older adults, suggestive of reduced interhemispheric distinctiveness. What remains unknown is 1) whether more expansive and bilateral motor representations result in overlapping motor cortical maps for adjacent body parts and for the two hands; 2) whether reduced distinctiveness underlies age declines in uni- and bimanual dexterity, and 3) whether reduced distinctiveness is restricted to the motor system or also applies to somatosensory representations. Elucidating the mechanisms of age-related decline in manual dexterity and somatosensation is critical because activities of daily living require skilled actions that depend on these sensorimotor processes. Our current objective is to quantify distinctiveness of motor and somatosensory representations within cortical hemispheres (Aim 1) and across cortical hemispheres (Aim 2) in individuals aged 20 - 79 years, with age as a continuous variable. We will also evaluate whether distinctiveness of sensorimotor representations-and manual dexterity-can be improved with a targeted training intervention (Aim 3). Our pilot data provide compelling preliminary evidence that training interventions specifically improve individuated hand control during bimanual actions, and result in altered corpus callosum structure as well as more focal sensorimotor representations. Our novel approach integrates precise behavioral measurements and multiple brain imaging techniques in basic science and intervention-based experiments. If successful, this endeavor will elucidate the underlying mechanisms contributing to age-related declines in sensorimotor function, and has high potential to make a significant impact by extending work productivity and prolonging independent living in older adults.